import java.util.Scanner;  
  
public class FactorialCalculator {
    public static int f(int n){
        if(n<=2){
            return 1;
        }
        return f(n-2)+f(n-1);

    }
    public static void main(String[] args) {  
        Scanner scanner = new Scanner(System.in);  
        System.out.print("请输入一个非负整数N: ");
        int n=scanner.nextInt();
       int sum=f(n);
        System.out.println(sum);
    }  
}